Safety valve for protecting hydraulic mine props against overloads

ABSTRACT

A safety valve which is adapted to protect hydraulic mine props against overloads. This valve has an elastomeric block which is supported at one end by a gas pressure cushion and the other end engages a seat and is adapted to regulate slots on the seat through which the liquid pressure medium can flow out of the pressure chamber of the prop.

United States Patent SAFETY VALVE FOR PROTECTING HYDRAULIC MINE PROPS AGAINST OVERLOADS 6 Claims, 1 Drawing Fig.

US. Cl 137/516.29, 137/529, 137/543.19

Int. Cl E21d15/51, F16k 15/02 Field of Search 137/469,

[56] References Cited UNITED STATES PATENTS 1,623,431 4/1927 McVoy 137/529X 2,556,867 6/1951 Carlisle et a1 137/529X 2,595,012 4/1952 Smith 251/332X 2,912,001 11/1959 Green 137/516.29

Primary Examiner-William F. ODea Assistant Examiner-Richard Gerard AttorneyMalco1m W. Fraser ABSTRACT: A safety valve which is adapted to protect hydraulic mine props against overloads. This valve has an elastomeric block which is supported at one end by a gas pressure cushion and the other end engages a seat and is adapted to regulate slots on the seat through which the liquid pressure medium can flow out of the pressure chamber of the prop.

SAFETY VALVE FOR PROTECTING HYDRAULIC MINE PROPS AGAINST OVERLOADS BACKGROUND OF THE INVENTION The closing element of such safety valves is considerably more elastic than the closing element of the otherwise usual valves which are braced by a spring. For this reason the closing elements of these so-called gas pressure valves can be deformed locally and free a path for capillary currents of liquid from the pressure chamber outwardly from the prop. The masses which have to be moved in this connection are considerably smaller than with the conventional rigid closing elements. The characteristic curve of the prop is for this reason on the whole more favorable.

Closer investigations of the behavior of hydraulic mine props equipped with such safety'valves show that the prop endures heavy loads which are applied in sudden bursts without permanent deformation. If, however, heavy loads are applied slowly onto the prop, the overload valve acts in response and the prop is lowered. Between these two cases of loading there exists a third case of loading. In this case, a heavy load is applied to the prop with great velocity. Then a permanent deformation of the prop takes place. The result of further considerations is that this simulated case of loading on the test bench is also conceivable in practice. It can, for example, occur during rock bursts which take place with a breading away of roof strata of comparatively large extent with correspondingly heavy weight.

So-called rock burst safety valves are known, but are con sidered superfluous by some experts (see Spruth Strebeausbau in Stahl and Leichtmetall", Verlag Glueckauf G.m.b.I-I., Essen, 1963, p. 102 and following), because, according to the opinion of these experts permanent deformations of the prop can be explained as being caused by it having been given the wrong dimensions. This has, on the other hand, not prevented the development of rock burst valves for mine props.

A rock burst valve, for example, is known which consists of two conventional pressure relief valves of varying cross section in which construction the valve with the larger cross section is intended for the high pressure occurring in the liquid pressure medium due to rock bursts (German published specification No. 1,078,516). In addition, it is known to arrange the large cross section required for compensating the high pressures occurring in the liquid pressure medium during rock bursts, by opening the exhaust valve of the prop by making provision for additional piston ring surface on this valve body (German published specification No. 1,195,251

These known proposals are not applicable to valves which operate with a gas pressure valve. On the other hand, however, the need for a solution to this difficulty is urgent, viz, how to provide such a gas pressure valve with a safety device for the above explained case of loading which up to the present has led to permanent deformation and hence to damage of the hydraulic mine prop.

SUMMARY OF THE INVENTION The invention overcomes these problems in that the block is movably guided in an axial direction inside a hollow piston which on its annular surface and supported on the seat is provided with grooves and in that the ability of the block to move axially within the hollow piston is sufficient in order to permit the surface facing the annularly constructed seat to be withdrawn behind the grooves in the hollow piston.

This safety valve acts under normal loads like a conventional gas pressure valve, that is to say by means of elastic deformation of the block in order to release the capillary currents of liquid pressure medium. With large loads occurring in sudden bursts the known property of hydraulic props to endure such loads elastically does not change. But as soon as a large load exceeding the carrying capacity of the prop is applied with great velocity, the block as a whole is lifted off the seat of the valve and opens the path for a correspondingly strong current of liquid from the pressure chamber outwardly of the prop. Such a strong flow of liquid pressure medium flowing at considerable speed would under normal circumstances on account of its eroding ability destroy the elastic block. The invention prevents this because the elastic block is able to withdraw behind the grooves. The invention therefore achieves the result of a complete safeguarding of the prop against load with the aid of a novel safety valve while at the same time avoiding excessive loads on vital parts of this valve.

In detail the arrangement can be made in such a manner that the hollow piston receives a guide piston which braces the block and together with the guide piston encloses the chamber which contains the gas pressure cushion.

This arrangement makes it possible to add to the two previously mentioned opening stages of the valve, a third one. In this third opening stage not only is the elastic block complete ly lifted from the seat, but in addition the annular surface of the guide piston provided with slots is lifted off its seat. This is in detail achieved in that, in order to limit the axial movement of the block in the hollow piston, provision is made on the hollow piston and on the guide piston for stops which support each other, and in that the hollow piston can be deflected against the pressure of the gas cushion and if necessary against a supporting spn'ng.

Such supporting spring becomes necessary when the effective surface of the guide piston which is subjected to the gas pressure happens to be comparatively small. Under such circumstances it is advisable to let the supporting spring act upon the guide piston and to provide on the guide piston and hollow piston supporting surfaces with the aid of which the guide piston can deflect the hollow piston after having lifted it from its seat, against the spring.

BRIEF DESCRIPTION OF THE DRAWING The FIGURE is a longitudinal sectional view of the safety valve showing the characteristics of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The safety valve has a housing 1 which has a portion 2 of reduced dimensions. The housing can be fitted with the part 2 extending into a drill hole provided in a hydraulic mine prop where it is locked in position. Then there is provided a sealed connection to the pressure chamber of the prop, and among other elements for this purpose, an O-shaped ring 3 may be provided on the outer surface of the housing portion 2. The housing 1 is closed at one end by a screw-threaded closure cap 4 which is sealed to the housing 1 by a sealing ring 5.

Within the housing is, according to the illustrated embodiment, an axially movable hollow piston 6 in which a guide piston 7 is axially movable. The hollow piston 6 is equipped at its end with a block 10 of elastomeric material, for example of plastic or some other material having a suitable coefficient of elasticity. The block I0 bears at one end against an annular seat 11. A washer 9 is interposed between the end of the block 10 and the guide piston 7 and an O-ring I2 provides a seal between the block 10 and the inner walls of the hollow piston 6.

In the illustrated embodiment the block 10 is screwed onto the guide piston 7 by means of a thread 13. For the assembly of the valve, the block 10, washer 9 and the O-ring 12 are introduced from the left-hand side into the hollow piston 6. The guide piston 7 has an O-ring 8 which seals against the walls of the hollow piston 6 and this assembly can be inserted into the hollow piston.

In the housing 1 is chamber 14 disposed between the closure cap 4 and the two pistons 6 and 7 constituting a gas pressure cushion containing a gas under high pressure. The gas is introduced to the chamber 14 through the drill hole 15 which is sealed by a disc 16 provided with an O-ring 17 and having a guide extension projecting into the hole.

A coil spring 18 exerts pressure against the guide piston 7 and in turn urges the block 10 through the washer l6 against the annular seat ll. lf desired a spring (not shown) may be arranged between the cap 4 and the hollow piston 6 for urging it against the seal 11. Normally the elastomeric block l and the hollow piston 6 are urged against the seat 11 by the high pressure gas in the chamber 14. At 9 and 20 there are provided, on the guide piston 7 and on the hollow piston 6, support surfaces with the aid of which the guide piston 7 can deflect the hollow piston 6 against the gas cushion after the hollow piston has been lifted off the seat. The numeral 19 designates shoulders arranged on the guide piston 7 and on the hollow piston 6. These shoulders do not abut against each other when the biock l0 and the hollow piston 6 are pressed onto the seat ll. The parts 7, 8, 9, l0 and 12 can shift within the hollow piston 6, according to the drawing, towards the right, until the washer 9 which forms a stop face and an additional stop shoulder 20 abut against each other at the hollow piston and in that manner limit the axial movement of the block 10 in the hollow piston 6. I

This axial movement of the block 10 within the hollow piston 6 is sufficient to withdraw its surface 23 which faces the annularly shaped seat ll behind several radial slots 21 in the ring-shaped surface of the hollow piston 6 which faces the annular seat and in this manner to withdraw the block 10 from the direct action of the flowing pressure medium.

Normally, a seal 24 seals the chamber 14 against a discharge port 22 in the housing 1 through which the liquid pressure medium can escape after passing through the slots 21.

In the drawing, the parts are illustrated in the positions which they occupy as soon as the gas chamber 14 is filled and no excessive pressure of the liquid pressure medium has been built up in the prop. At this time the hollow piston 6 and the guide piston 7 abut against the annular seat 11. If the pressure of the liquid pressure medium in the pressure chamber of the prop rises beyond a fixed value, the elastomeric block 10 together with the guide piston 7 which braces the sleeve move, a

in the illustration of the drawing, to the right. Then there is formed between the annular seat 111 and the block 10 a gap through which a small quantity of liquid can flow through the slots 21 in the ring-shaped surface of the hollow piston 6 and the grooves or slots 21a in the peripheral surface of the hollow piston and discharge from the valve through the port 22 in the housing.

If on account of a large and suddenly applied load, a sudden increase in the pressure of the liquid pressure medium in the pressure chamber of the prop takes place, the whole block 10 with its bracing guide piston 7 is lifted off the seat 11 and is at the utmost moved against the stop faces 20. In this case a very large cross section is cleared and therefore in the necessary short intervals the pressure in the pressure chamber of the prop can be lowered As the hollow piston 6 in turn is axially shiftable, this too can be moved from the seat 111. Consequently it is possible to bring about a third opening stage of the valve at which time even the front end of the hollow piston is lifted off the seat 1 1.

It should be observed that the pressure of the gas in the chamber 14 operates against a greater surface area as to the guide piston 7 than as to the hollow piston 6. Consequently upon deformation of the elastomeric block. It) by hydraulic pressure through the opening at the end of the housing 1, the slots 21 can be uncovered to release hydraulic pressure fluid without axial movement of the guide piston 7. However, due

to the differential gas pressures against the two pistons, the hollow piston can at this time move axially.

The technical advance which is achieved with the above described safety valve consists mainly in that the valve, while maintaining the particular advantages inherent in the gas pressure valves, protects the prop even during extraordinary loads which are encountered with rock burst.

lclaim:

l. A safety valve for protecting hydraulic mine props against overloads comprising a housin provided with an inlet opening at one end adapted to receive ydraulic pressure from a mine prop, a hollow piston having axial movement within said housing, means closing the opposite end of said housing, a chamber between said housing closing means and the end of said piston containing gas under pressure to provide a gas pressure cushion yieldably resisting retracting movement of said piston, an annular valve seat about said opening, an elastomeric block mounted for axial movement on the end of said piston and having an annular surface seating against said valve seat, a discharge opening in the sidewall of said housing spaced from said chamber, a seal between said piston and the walls of said housing to prevent the escape of gas from said chamber to said discharge opening, and slots in said piston extending from said valve seat to the region of said discharge opening to provide fluid communication between said inlet opening and said discharge opening, said gas pressure cushion resisting movement of said block away from said valve seat, said block being mounted for covering said slots and arresting flow therethrough in a valve closed position'and responsive to a predetermined pressure at said inlet opening to move to a valve open position uncovering said slots.

2. A safety valve as claimed in claim 1, in which the inner end of said hollow piston is cupped, a guide piston within said hollow piston and shiftable axially relative thereto and exposed to said gas pressure cushion, a connection between said guide piston and said elastomeric block to enable conjoint movement thereofland a seal between said guide piston and said hollow piston for militating against the escape of gas from said chamber.

3. A safety valve as claimed in claim 2 comprising a shoulder on said hollow piston, and a washer abutting the inner end of said elastomeric block and adapted to engage said shoulder upon axial movement of said block relative to said hollow piston, thereby to limit the movement of the block and guide piston assembly relative to said hollow piston and to cause said hollow piston to be shifted thereafter by the guide piston assembly.

4. A safety valve as claimed in claim 3, comprising facing abutment surfaces on said hollow piston and guide piston for limiting the axial movement of the hollow piston with respect to said guide piston and to enable the guide piston thereafter to be shifted by the hollow piston.

5. A safety valve as claimed in claim 4 in which the area ex posed to the pressure of the gas cushion is greater with respect to said guide piston, than said hollow piston, whereby said elastomeric block may be deformed to uncover said slots without moving axially but axial movement may at that time be imparted to said hollow piston for enabling hydraulic pressure release.

6. A safety valve as claimed in claim 2, comprising a coil spring interposed between said housing closing means and said guide piston. 

1. A safety valve for protecting hydraulic mine props against overloads comprising a housing provided with an inlet opening at one end adapted to receive hydraulic pressure from a mine prop, a hollow piston having axial movement within said housing, means closing the opposite end of said housing, a chamber between said housing closing means and the end of said piston containing gas under pressure to provide a gas pressure cushion yieldably resisting retracting movement of said piston, an annular valve seat about said opening, an elastomeric block mounted for axial movement on the end of said piston and having an annular surface seating against said valve seat, a discharge opening in the sidewall of said housing spaced from said chamber, a seal between said piston and the walls of said housing to prevent the escape of gas from said chamber to said discharge opening, and slots in said piston extending from said valve seat to the region of said discharge opening to provide fluid communication between said inlet opening and said discharge opening, said gas pressure cushion resisting movement of said block away from said valve seat, said block being mounted for covering said slots and arresting flow therethrough in a valve closed position and responsive to a predetermined pressure at said inlet opening to move to a valve open position uncovering said slots.
 2. A safety valve as claimed in claim 1, in which the inner end of said hollow piston is cupped, a guide piston within said hollow piston and shiftable axially relative thereto and exposed to said gas pressure cushion, a connection between said guide piston and said elastomeric block to enable conjoint movement thereof, and a seal between said guide piston and said hollow piston for militating against the escape of gas from said chamber.
 3. A safety valve as claimed in claim 2 comprising a shoulder on said hollow piston, and a washer abutting the inner end of said elastomeric block and adapted to engage said shoulder upon axial movement of said block relative to said hollow piston, thereby to limit the movement of the block and guide piston assembly relative to said hollow piston and to cause said hollow piston to be shifted thereafter by the guide piston assembly.
 4. A safety valve as claimed in claim 3, comprising facing abutment surfaces on said hollow piston and guide piston for limiting the axial movement of the hollow piston with respect to said guide piston and to enable the guide piston thereafter to be shifted by the hollow piston.
 5. A safety valve as claimed in claim 4 in which the area exposed to the pressure of the gas cushion is greater with respect to said guide piston than said hollow piston, whereby said elastomeric block may be deformed to uncover said slots without moving axially but axial movement may at that time be imparted to said hollow piston for enabling hydraulic pressure release.
 6. A safety valve as claimed in claim 2, comprising a coil spring interposed between said Housing closing means and said guide piston. 